The following information is provided to assist the reader in understanding the devices, systems and/or methods disclosed below and the environment in which such devices, systems and/or methods will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the devices, systems and/or methods or the background. The disclosure of all references cited herein are incorporated by reference.
A supplied-air respirator such as self-contained breathing apparatus (SCBA) permits a person to breath in hazardous environments such as fires and confined spaces where breathing would be difficult or impossible without mechanical aid. A supplied-air respirator may, for example, include a full facepiece, a harness and carrier assembly, an air cylinder full of high pressure compressed air for breathing and at least one, and more typically two, air-pressure regulators. The first or first-stage regulator is typically mounted near the air cylinder and functions to reduce the relatively high pressure of the compressed air from the air cylinder to above atmospheric pressure. The air cylinder typically contains air or gas under high pressure (for example, 2200 psi to 4500 psi). The first stage regulator may, for example, reduce the pressure to about 80-100 psi. The second or second-stage regulator is typically mounted on the facepiece and functions to adjust the flow of air to meet the respiratory needs of the user. Respiration-controlled regulator assemblies are disclosed, for example, in U.S. Pat. Nos. 4,821,767 and 5,016,627.
The facepiece or face mask, which is sealed to the face of the user, typically includes a lens through which the user can view the surrounding environment. The facepiece also includes a port or mount for fluid connection with the second-stage regulator through which inspired air passes into the face mask and an exhalation port through with expired air passes out of the mask. In some facepieces, a single port is used for both inspired and expired air. In other facepieces, separate ports are used. The user's respiration controls a valve system (for example, including an inhalation valve and an exhalation valve) to control delivery of pressurized air via the second-stage regulator. Often, it is desirable to maintain a slight positive pressure within the facepiece relative to ambient pressure. Facepieces for supplied-air respirators in which a positive pressure is maintained within the facepiece are often referred to as pressure demand facepieces, while other facepieces for supplied-air respirators are often referred to as demand facepieces.
The valve system of many facepieces results in resistance to inhalation and exhalation (which must be overcome by the user) when the facepiece is used without the pressure regulator in place (often referred to as a “stand-by” or “ambient” mode of operation). In the case of pressure demand facepieces, the exhalation valve is biased in a closed position (for example, spring-loaded) to maintain a slight positive pressure during normal operation thereof, exacerbating exhalation resistance as compared to demand facepieces. The resistance to inhalation and exhalation can result in discomfort and fatigue for the user.
A number of facepieces have provided open ports therein such that respiration can occur generally without restriction when that the facepiece is used in the stand-by mode (that is, without the pressure regulator in connection therewith). However, such ports usually result in contamination of the pressure regulator, which is undesirable because pressure regulators are often shared between users.